As fluororubbers obtained from fluorinated polymers, for example, a fluororesin such as polytetrafluoroethylene, a tetrafluoroethylene/hexafluoropropylene copolymer or a tetrafluoroethylene/ethylene copolymer, a vinylidene fluoride/hexafluoropropylene copolymer, a tetrafluoroethylene/propylene copolymer and a tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer are known.
As these fluororubbers are excellent in heat resistance and chemical resistance, they are used in a sever condition where normal materials are not durable. However, among them, a vulcanizate of a copolymer having many repeating units based on vinylidene fluoride, such as a fluororubber obtained by copolymerizing vinylidene fluoride and hexafluoropropylene, so-called FKM, or a fluororubber obtained by copolymerizing vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene, has a problem such that its durability against a high heat resistance engine oil having e.g. an amine type antiaging agent added, is insufficient, because its resistance against a base is not enough and its degree of degradation caused by the reaction of an amine type additive with the moiety of repeating units based on vinylidene fluoride is high (Patent Document 1).
On the other hand, a fluororubber obtained by copolymerizing tetrafluoroethylene and propylene, so-called FEPM, is excellent in resistance against a base, as compared with FKM. Further, it is known that the fluororubber is excellent in durability also against a high heat resistance engine oil comprising, for example, an amine type additive (Patent Document 2). However, when FEPM is crosslinked by a polyol crosslinking recipe using a polyhydroxy compound and a crosslinking accelerator in combination, the crosslinking reactivity is low as compared with FMK, and various crosslinking recipe have been proposed to speed up the crosslinking (Patent Document 3).
Patent Document 1: JP-A-6-306244
Patent Document 2: JP-A-6-306242
Patent Document 3: JP-A-12-281856